The present invention relates to automatic fire sprinkler systems for buildings, and particularly to a method for locating leaks in the normally dry portions of the piping of such systems.
For various reasons, including the desire to avoid corrosion and the possibility of water freezing within sprinkler pipes in unheated locations, automatic fire sprinkler systems often include a dry-pipe portion. Normally, the dry-pipe portion of such a sprinkler system contains air at a pressure sufficiently above atmospheric pressure to hold a pneumatically-controlled water control valve in a closed condition which prevents fire main pressure from forcing water into the dry-pipe portions of the sprinkler system. For example, in a commonly used system a pressure of 40 psig in the dry portions of the sprinkler system is normally used to keep the fire main water valve closed. The 40 psig pressure includes a safety factor, and ordinarily the pressure can drop as low as about 20 psig without allowing the water control valve to open; however, if the air pressure in the "dry" side falls to a low enough value the water control valve will open, allowing water to enter the normally dry piping. So long as the normally dry piping is airtight, the air pressure in that piping will remain high enough to hold the water pressure control valve closed, with only infrequent monitoring, such as a monthly check of pressure, being required.
Ordinarily, the sprinkler heads in the dry portion of such a system are sealed by heat-fusible plugs. When a fire occurs in the area protected by the sprinkler system the heat of the fire will fuse the plugs of sprinkler heads in the vicinity of the fire, allowing air pressure to escape. This release of pressure permits the water control valve to open and begins sprinkling of the fire through the affected sprinkler heads.
When the normally dry piping is not airtight, the normally present 40 psig air pressure within the normally dry piping falls gradually until the water control valve opens. Water under the pressure of the fire main then enters the normally dry portion of the sprinkler system. In warm climates this is not ordinarily a particularly serious problem. However, where there are leaks large enough to permit air pressure to be lost, water under the higher fire main pressure of 150 psig, for example, may leak in amounts great enough to cause damage.
What is more significant, however, is that in climates where freezing weather is possible or probable the normally water-filled portion of a sprinkling system is insulated or located within a heated portion of a building, but the normally dry portions may not be in heated locations. Water entering such portions of the sprinkler piping system may quickly freeze, with two potentially dangerous results. First, the pipes blocked by ice are incapable of providing water to sprinkle a fire should one occur. Second, and more common, pipes may be split by the freezing water, so that when the ice is thawed significant amounts of water damage may occur in the vicinity of such pipe failures. It is therefore very desirable to prevent the inadvertent opening of the water control valve in such a fire sprinkler system.
It has previously been very difficult to identify the location of minute leaks which can release air at a rate great enough to gradually reduce the air pressure in the "dry" portions of a sprinkler system below the minimum required to prevent the water control valve from opening. Such leaks may often be too small to be detected by the use of soap bubbles, or by hearing the outward rush of air through pinholes or cracks in the affected piping. While a hydrostatic test may quickly reveal the presence of leaks, it may not locate them, and a periodic check of pressure gauges is similarly ineffective in locating the opening through which air pressure is lost from the normally dry portions of a sprinkler system. It has therefore previously taken much experimentation and time to locate leaks in fire sprinkler systems of this type.
A part of the problem is that the air normally used to pressurize the normally dry portions of a fire sprinkler system can escape through holes through which ordinary water normally will not pass. Thus, even filling the pipe with water under pressure may not be effective to detect the location of leaks. This is particularly likely to be the case in humid weather, where filling the normally dry pipe with water may well result in the exterior surfaces of the piping becoming covered with water droplets, none of which actually originates from within the piping.
The general problem of detecting leaks in piping has been addressed in Packo U.S. Pat. Nos. 3,483,735 and 3,572,085. Packo teaches the use of visual indicant gas and similar agents which become visible as a color or smoke, or may be detected under ultraviolet or infrared detectors to provide an indication that a leak exists. The use of such gaseous mixtures in an installed fire sprinkling system, however, may be unduly difficult and can produce only a temporary indication of the location of a leak.
Burton, Jr. et al., U.S. Pat. No. 3,683,675, discloses a method of leak detection in which material is dispersed within a gaseous mixture inside a tank or container to be checked for leaks. However, this system is inapplicable for testing already-installed piping such as the normally dry portions of a sprinkler system, since it requires visual inspection of the interior of the container to detect the location of openings through which gas may escape.
What is needed, therefore, is a safe method for detecting the location of leaks in a gas-containing portion of a system such a fire sprinkler system. Such a method should be simple to use, provide an externally visible indication of the location of a leak, include only nontoxic and noncorrosive materials, and be reliably useful for locating extremely small openings.